JP2010170826A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell improved in output performance. <P>SOLUTION: The fuel cell has a cathode catalyst layer 5, an anode catalyst layer 7, an electrolyte membrane 2 which is formed between the cathode catalyst layer 5 and the anode catalyst layer 7, and an anode gas diffusion layer 8 which is laminated on the anode catalyst layer 7 and includes first to third water repellent porous layers 9, 11, 12. The air permeability resistivity of the first water repellent porous layer 9 is larger than that of the second water repellent porous layer 11, and the total of the air permeability resistivity of the first water repellent porous layer 9 and the second water repellent porous layer 11 is larger than that of the third water repellent porous layer 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell, and is particularly suitable for a small liquid fuel direct supply type fuel cell.

  In recent years, small fuel cells have attracted attention in place of lithium ion secondary batteries. In particular, a direct methanol fuel cell (DMFC) using methanol as a fuel is more difficult to handle hydrogen gas than a fuel cell using hydrogen gas, and the organic fuel is reformed to generate hydrogen. There is no need for a device to create and it is excellent in miniaturization.

  In DMFC, methanol is oxidized and decomposed at an anode (for example, a fuel electrode) to generate carbon dioxide, protons, and electrons. On the other hand, in the cathode (for example, the air electrode), water is generated by oxygen obtained from air, protons supplied from the fuel electrode through the electrolyte membrane, and electrons supplied from the fuel electrode through an external circuit. In addition, power is supplied by electrons passing through the external circuit.

  Patent Documents 1 to 3 describe that one or two or more layers containing carbon are interposed between the catalyst layer and the diffusion layer. Patent Document 4 describes the use of carbon cloth for the gas diffusion layer.

JP 2004-214173 A JP 2005-1000074 A JP 2006-120508 A JP 2007-317391 A

  The present invention seeks to provide a fuel cell with improved output performance.

The fuel cell according to the present invention comprises a cathode catalyst layer,
An anode catalyst layer;
An electrolyte membrane disposed between the cathode catalyst layer and the anode catalyst layer;
An anode gas diffusion layer including first to third water-repellent porous layers laminated on the anode catalyst layer,
The air permeability resistance of the first water repellent porous layer is larger than the air resistance resistance of the second water repellent porous layer, and the first water repellent porous layer and the second water repellent porous layer. The total air resistance of the aqueous porous layer is larger than that of the third water repellent porous layer.

  According to the present invention, it is possible to provide a fuel cell with improved output performance.

Sectional drawing of the membrane electrode assembly used for the fuel cell of this embodiment. FIG. 3 is a schematic cross-sectional view for explaining a method for producing the first and second water-repellent porous layers of Example 1. Sectional drawing which shows the fuel cell of this embodiment. The perspective view which shows the fuel distribution mechanism of the fuel cell of FIG. Schematic diagram of Oken type (back pressure type) air permeability resistance measuring machine. The schematic diagram regarding the flow path of the measuring machine of FIG. The schematic diagram about the flow path of a Gurley type measuring machine. The schematic diagram for demonstrating the measuring method of the air resistance of a 1st-3rd water-repellent porous layer. Sectional drawing which shows the membrane electrode assembly used for the fuel cell of the comparative example 4. FIG. 3 is a schematic diagram showing fuel and water distribution in the first to third water-repellent porous layers in Example 1. FIG. 5 is a schematic diagram showing fuel and water distribution in the first to third water-repellent porous layers in Example 2. The schematic diagram which shows the fuel and water distribution of the 1st-3rd water-repellent porous layer in the comparative example 2. FIG. The characteristic view which shows the relationship between the operation time and output density in the fuel cell of Examples 1-2 and Comparative Examples 1-4.

  The fuel cell according to the present invention includes an anode gas diffusion layer including first to third water-repellent porous layers laminated on an anode catalyst layer. The first water-repellent porous layer is laminated on the anode catalyst layer, and the second and third water-repellent porous layers are arranged in this order outside the first water-repellent porous layer. The air resistance of the first water-repellent porous layer is made larger than the air resistance of the second water-repellent porous layer, and the first water-repellent porous layer and the second water-repellent porous layer When the water generated in the cathode catalyst layer by power generation is supplied to the anode catalyst layer through the electrolyte membrane by increasing the total air resistance of the porous layer compared to the third water repellent porous layer, Water can be retained in the vicinity of the anode catalyst layer.

  In addition, since the fuel is supplied from the third water-repellent porous layer side, the air resistance of the first water-repellent porous layer is compared with the air resistance of the second water-repellent porous layer. Supply of fuel by increasing the total air resistance of the first water repellent porous layer and the second water repellent porous layer as compared to the third water repellent porous layer. Can be made smooth.

  As a result, since the fuel and water can be mixed properly, the output performance of the fuel cell can be improved.

  Hereinafter, a membrane electrode assembly used in a fuel cell according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, a membrane electrode assembly (MEA) 1 includes an electrolyte membrane 2, a cathode 3, and an anode 4. The cathode 3 has a cathode catalyst layer 5 laminated on one surface of the electrolyte membrane 2 and a cathode diffusion layer 6 laminated on the cathode catalyst layer 5. On the other hand, the anode 4 has an anode catalyst layer 7 laminated on the other surface of the electrolyte membrane 2 and an anode diffusion layer 8 laminated on the anode catalyst layer 7. The anode diffusion layer 8 includes, from the anode catalyst layer 7 side, a first water-repellent porous layer 9, a conductive substrate 10, a second water-repellent porous layer 11, and a third water-repellent porous layer 12. It consists of what is laminated and integrated in order.

  Hereinafter, each member will be described.

1) First water-repellent porous layer 9 and second water-repellent porous layer 11
Each water repellent porous layer preferably contains a water repellent such as a fluororesin such as polytetrafluoroethylene (PTFE).

  Each water repellent porous layer preferably contains a conductive substance in order to reduce its electrical resistance. Examples of the conductive substance include a carbon material. Examples of the carbon material include ketjen black, print tex, and carbon nanotube, and the carbon material is not particularly limited as long as it is in the form of particles (for example, spherical particles, flat particles) or fibers. In particular, fine particles of carbon material or nanofibers of carbon material are suitable.

The air resistance of each water-repellent porous layer is desirably 30 gale seconds or more. Further, when the air permeability resistance of the first water repellent porous layer is T ₁ and the air resistance of the second water repellent porous layer is T ₂ , T ₂ / T ₁ is 90% or less. It is preferable that

  Each water repellent porous layer is desirably integrated with a conductive substrate. Specifically, the first water-repellent porous layer 9 is integrated on one surface of the conductive substrate 10 and the second water-repellent porous layer 11 is integrated on the other surface. Is preferred. For the conductive substrate 10, for example, carbon paper can be used.

  The first and second water-repellent porous layers 9 and 11 integrated with the conductive substrate 10 are produced, for example, by the method shown in FIG. That is, after preparing a slurry by mixing a water repellent and a conductive material, the obtained slurry was applied to both surfaces of the conductive substrate 10 by a spray coating method, and then dried with warm air or naturally at room temperature, The slurry is applied over only one surface of the conductive substrate 10. By baking this, the 1st, 2nd water-repellent porous layers 9 and 11 integrated with the electroconductive base material are obtained.

2) Third water repellent porous layer 12
The third water repellent porous layer 12 includes a conductive substrate and a porous film formed on the conductive substrate and containing a carbon material and a water repellent. The third water-repellent porous layer 12 is desirably arranged so that the porous film is in contact with the second water-repellent porous layer 11.

  Examples of the conductive substrate include carbon cloth.

  Examples of the water repellent and the carbon material include the same as those described in the first and second water repellent porous layers 9 and 11 described above.

  The air permeability resistance of the third water repellent porous layer 12 is desirably less than 30 gale seconds.

  The third water repellent porous layer 12 is produced, for example, by the method shown in FIG. That is, after preparing a slurry by mixing a water repellent and a conductive material, the obtained slurry is applied to one side of a conductive substrate by a spray coating method, dried with warm air or naturally dried at room temperature, and then fired. Thus, the third water repellent porous layer 12 is obtained.

3) Cathode catalyst layer 5, anode catalyst layer 7 and electrolyte membrane 2
Examples of the catalyst contained in the cathode catalyst layer 5 and the anode catalyst layer 7 include platinum group elements such as single metals such as Pt, Ru, Rh, Ir, Os, and Pd, and alloys containing platinum group elements. Can be mentioned. Specifically, platinum, Pt—Ni, or the like is used as a catalyst on the air electrode side, such as Pt—Ru or Pt—Mo having strong resistance to methanol or carbon monoxide as the fuel electrode side catalyst. Although preferable, it is not limited to these. Further, a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst may be used.

  Examples of the proton conductive material contained in the cathode catalyst layer 5, the anode catalyst layer 7 and the electrolyte membrane 2 include, for example, a fluorine-based resin having a sulfonic acid group (trade name Nafion (registered trademark) manufactured by DuPont, Asahi Glass Co., Ltd.). For example, a perfluorosulfonic acid polymer such as Flemion (registered trademark), a hydrocarbon resin having a sulfonic acid group, an inorganic substance (for example, tungstic acid, phosphotungstic acid, lithium nitrate, etc.). However, it is not limited to these.

4) Cathode gas diffusion layer 6
The cathode gas diffusion layer 6 serves to uniformly supply the oxidant to the cathode catalyst layer 5 and also serves as a current collector for the cathode catalyst layer 5. For the cathode gas diffusion layer 6, for example, carbon paper or carbon cloth subjected to water repellent treatment can be used. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

  A conductive layer is laminated on the anode gas diffusion layer 8 and the cathode gas diffusion layer 6 as necessary. As these conductive layers, for example, a porous layer (for example, mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) is coated with a highly conductive metal such as gold. Composite materials and the like are used.

  A fuel cell provided with the membrane electrode assembly shown in FIG. 1 will be described with reference to FIGS.

  The fuel cell shown in FIG. 3 includes a membrane electrode assembly 1 shown in FIG. 1, a fuel distribution mechanism 20 that supplies fuel to the membrane electrode assembly 1, a fuel storage unit 21 that stores liquid fuel, and these fuel distributions. It is mainly composed of a flow path 22 that connects the mechanism 20 and the fuel storage portion 21.

Rubber O-rings 24 are interposed between the electrolyte membrane 2 and the fuel distribution mechanism 20 and the cover plate 23, respectively, thereby preventing fuel leakage and oxidant leakage from the membrane electrode assembly (MEA) 1. It is preventing. Although not shown, the cover plate 23 has an opening for taking in air as an oxidant. A surface layer is disposed between the cover plate 23 and the membrane electrode assembly 1 as necessary. The surface layer adjusts the amount of air taken in, and has a plurality of air inlets whose number, size, etc. are adjusted according to the amount of air taken in. By providing such a cover plate 23, the oxidant can be naturally supplied to the cathode 3 without using a blower for supplying the oxidant. Note that the oxidizing agent is not limited to air, and a gas containing O ₂ can be used.

  A water vapor permeation suppression layer is disposed between the cover plate 23 and the membrane electrode assembly 1 as necessary. The water vapor permeation suppression layer is impregnated with a part of the water generated in the cathode catalyst layer 5 to suppress water evaporation and promote uniform diffusion of air to the cathode catalyst layer 5. Examples of the water vapor permeation suppressing layer include polyethylene-based polymer, polyolefin-based polymer, polyurethane-based polymer, polypropylene-based polymer, polyester-based polymer, fluorine-based polymer, or polyimide-based polymer porous film. it can. Specific examples include water vapor permeation suppression layers such as Nitto Denko's trade name Sunmap and DuPont's trade name PTFE.

  The fuel storage unit 21 stores liquid fuel corresponding to the membrane electrode assembly 1. Examples of the liquid fuel include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel is not necessarily limited to methanol fuel. The liquid fuel may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, liquid fuel corresponding to the membrane electrode assembly 1 is stored in the fuel storage portion 21.

  The type and concentration of the liquid fuel are not limited. However, the characteristic of the fuel distribution mechanism 20 having the plurality of fuel discharge ports 25 becomes more apparent when the fuel concentration is high. For this reason, the fuel cell can particularly exhibit its performance and effects when a methanol aqueous solution or pure methanol having a concentration of 80% or more is used as the liquid fuel. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (A) occurs.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Formula (A)
Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 2 and reach the cathode catalyst layer 5. The air supplied to the cathode catalyst layer 5 from the opening of the cover plate 23 causes a reaction represented by the following formula (B). By this reaction, water is generated and a power generation reaction occurs.

(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Formula (B)
A fuel distribution mechanism 20 is arranged on the anode (fuel electrode) 4 side of the membrane electrode assembly 1. The fuel distribution mechanism 20 is connected to a fuel storage portion 21 via a liquid fuel flow path 22 such as a pipe. Liquid fuel is introduced into the fuel distribution mechanism 20 from the fuel storage portion 21 through the flow path 22. The flow path 22 is not limited to piping independent of the fuel distribution mechanism 20 and the fuel storage unit 21. For example, when the fuel distribution mechanism 20 and the fuel storage unit 21 are stacked and integrated, a liquid fuel flow path connecting them may be used. The fuel distribution mechanism 20 only needs to be connected to the fuel storage portion 21 via the flow path 22.

  The mechanism for sending the liquid fuel from the fuel storage unit 21 to the fuel distribution mechanism 20 is not particularly limited. For example, when the installation location at the time of use is fixed, the liquid fuel can be dropped from the fuel storage unit 21 to the fuel distribution mechanism 20 and fed by using gravity. Further, by using the flow path 22 filled with a porous body or the like, the liquid can be fed from the fuel storage portion 21 to the fuel distribution mechanism 20 by a capillary phenomenon. Furthermore, liquid feeding from the fuel storage unit 21 to the fuel distribution mechanism 20 may be performed by a pump 26 as shown in FIG. Alternatively, as long as the fuel is supplied from the fuel distribution mechanism 20 to the membrane electrode assembly 1, a fuel cutoff valve may be arranged instead of the pump 26. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  As shown in FIG. 4, the fuel distribution mechanism 20 includes at least one fuel inlet 27 through which liquid fuel flows through the flow path 22 and a plurality of fuel outlets 25 through which the liquid fuel and its vaporized components are discharged. The fuel distribution plate 28 having As shown in FIG. 3, a gap 29 serving as a liquid fuel passage led from the fuel injection port 27 is provided inside the fuel distribution plate 28. The plurality of fuel discharge ports 25 are directly connected to gaps 29 that function as fuel passages.

  The liquid fuel introduced into the fuel distribution mechanism 20 from the fuel inlet 27 enters the gap portion 29 and is led to the plurality of fuel discharge ports 25 through the gap portion 29 functioning as the fuel passage. For example, a gas-liquid separator (not shown) that transmits only the vaporized component of the liquid fuel and does not transmit the liquid component may be disposed in the plurality of fuel discharge ports 25. As a result, the vaporized component of the liquid fuel is supplied to the anode 4 of the membrane electrode assembly 1. The gas-liquid separator may be installed as a gas-liquid separation membrane or the like between the fuel distribution mechanism 20 and the anode 4. The vaporized component of the liquid fuel is discharged from a plurality of fuel discharge ports 25 toward a plurality of locations on the anode 4.

A plurality of fuel discharge ports 25 are provided on the surface of the fuel distribution plate 28 facing the anode 4 so that fuel can be supplied to the entire membrane electrode assembly 1. The number of the fuel discharge ports 25 may be two or more. However, in order to equalize the fuel supply amount in the surface of the membrane electrode assembly 1, 0.1 to 10 / cm ² fuel discharge ports 25 are provided. It is preferable to form it so that it exists.

  The liquid fuel introduced into the fuel distribution mechanism 20 described above is guided to the plurality of fuel discharge ports 25 via the gaps 29. Since the gap portion 29 of the fuel distribution mechanism 20 functions as a buffer, fuel of a specified concentration is discharged from each of the plurality of fuel discharge ports 25. Since the plurality of fuel discharge ports 25 are arranged so that fuel is supplied to the entire surface of the membrane electrode assembly 1, the amount of fuel supplied to the membrane electrode assembly 1 can be made uniform.

The air resistance of the water repellent porous layer will be described. The air resistance is measured by a Oken type air permeability tester. The Gurley second, which is the unit of air resistance, is based on the Gurley method (JIS P8117). A paper (sample) with 100 cm ³ of air and a width of 64.5 cm ² under a pressure difference of 0.0132 Kgf / cm ² is used. Means time (seconds) to pass.

  The standard of the Oken air permeability tester is J. TAPPI NO5B (standard of paper pulp technology), and the model is EGO-2S. The diameter of the measurement end is φ30 mm and the nozzle type name is G, 100, or φ10 mm and the nozzle type name is 1 / 10G, 100.

  The measurement principle will be described below with reference to FIGS.

  FIG. 5 is a schematic diagram of an Oken type (back pressure type) air permeability measuring machine. A measurement sample 102 (for example, an anode porous layer) is disposed at the measurement end 101. A water column pressure gauge 104 is connected to the measurement end 101 via a thin tube 103. The water column pressure gauge 104 has a side pressure chamber (B chamber) 105 connected to the narrow tube 103 and a constant pressure chamber (A chamber) 107 connected via a thin tube 106 called a nozzle. A constant pressure chamber (A chamber) 107 of the water column pressure gauge 104 is connected to an external compression source 109 via a thin tube 108. The thin tube 108 is provided with a pressure gauge 110.

  Air pressure supplied from the external compression source 109 through the pipe 108, the constant pressure chamber (A chamber) 107, the narrow tube 106, the side pressure chamber (B chamber) 105, and the narrow tube 103 is applied to the measurement sample 102. The air pressure when supplied from the external compression source 109 is measured by the pressure gauge 110. The pressure applied to the surface opposite to the side where the air pressure is applied is maintained at atmospheric pressure.

The air pressure that passes through the measurement sample 102 is measured by a water column pressure gauge 104. The gas permeability _TG of the measurement sample 102 is obtained based on the principle described below.

  FIG. 6 is a schematic diagram relating to the flow path of the measuring machine of FIG. In FIG. 6, the same members as those described in FIG. 5 are denoted by the same reference numerals, but the narrow tube 111 connected to the right side of the side pressure chamber (B chamber) 105 looks like the measurement sample 102. It is.

  Regarding FIG. 6, when the flow in both capillaries is laminar, the relationship between flow rate and differential pressure follows Hagen-Poiseuille's law. Further, when the flow velocity is small, a continuous law can be applied to the flow path system.

Q _C = Q = π / 8 μ · (P _C −P) · R ⁴ / L (1)
Q = π / 8μ · P · r ⁴ / l (2)
P _C is the pressure in the constant pressure chamber (A chamber) 107 and is maintained at a constant pressure of 500 mmH ₂ O, P is the pressure in the side pressure chamber (B chamber) 105, and Q _C is the flow rate (cm ³ / sec), Q is the flow rate (cm ³ / sec) in the narrow tube 111, L is the length (mm) of the nozzle 106, l is the length (mm) of the narrow tube 111, and R is the inner diameter (mm) of the nozzle 106. ) Where r is the inner diameter (mm) of the narrow tube 111 and μ is the viscosity coefficient of air.

Figure 7 is a schematic diagram of the flow path of Gurley measuring instrument shows that the air in the G chamber 112 is maintained at a constant pressure P _G is released into the atmosphere through tubules 113. The thin tube 113 is an example of the measurement sample 102. The G chamber 112 and the narrow tube 113 in FIG. 7 follow the same rules as described in FIG.

Q _G = π / 8μ · P _G · r ⁴ / l (3)
T _G = 100 / Q _G (4)
P _G = 4 W / πD ² = 0.0132 (kgf / cm ² ) = 1.29 (kPa) (5)
P _G is the inner cylinder of the measuring portion defined by JIS P8117 (W = 567g, D = 74mm) is calculated from. Q _G is the flow rate (cm ³ / sec) in the narrow tube 113 and _TG is the air permeability (sec).

From the above equations (1), (2), (3), (4), the relationship between _TG and P is given by the following equation (6). If the constant K of the measuring machine is determined, the air permeability _TG of the Gurley can be estimated directly on the water column pressure gauge of FIG.

T _G = 800 μ / πP _G · L / R ⁴ · P / (P _C -P)
= K · P / (P _C -P) (6)
Here, K is a measuring machine constant _{(K = 800μ / πP G ·} L / R 4), the length of capillary 106 L (mm) and an inside diameter R (mm) is defined on the design.

  In addition, when measuring air resistance by the said method, it measures by making the surface of a measuring object into the lower side, and obtains a measured value. For example, when measuring the air resistance of the second water-repellent porous layer 11, as shown in FIG. 8, the first and second water-repellent porous layers carried on both surfaces of the conductive substrate 10 are used. 9 and 11 are sandwiched between the O-rings 31 with the second water repellent porous layer 11 facing down, and the air resistance is measured.

  The fuel cell applicable to the present invention is an active type fuel cell in which liquid fuel and oxidant are supplied by using an auxiliary device such as a pump, and a passive type (internal) that supplies vaporized components of liquid fuel to the anode. (Vaporization type) fuel cell, semi-passive type fuel cell shown in FIGS. The active fuel cell employs a system in which a fuel made of an aqueous methanol solution is supplied to the anode of the MEA while being adjusted by a pump so that the amount thereof is constant, and air is also supplied to the cathode by a pump. In the passive type fuel cell, a system in which vaporized methanol is naturally supplied to the anode of the MEA and natural air is also supplied to the cathode and no extra equipment such as a pump is provided. In the semi-passive type fuel cell, the fuel supplied from the fuel storage part to the membrane electrode assembly is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage part. The semi-passive type fuel cell is different from the active method because it does not circulate the fuel, and does not impair the downsizing of the device. Further, the semi-passive type fuel cell uses a pump for supplying fuel, and is different from a pure passive type such as an internal vaporization type. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
<Preparation of slurry>
6.50 g of carbon material (commercial product, ValcanXC-72), 65.00 g of pure water, 1.30 g of surfactant (commercial product), 7.20 g of polytetrafluoroethylene (PTFE) solution (commercial product: concentration 60%) Were mixed with a stirrer dispersion for 80 minutes to obtain about 72 g of a slurry.

<Preparation of first and second water-repellent porous layers>
Commercially available carbon paper (manufactured by Toray: TGP-H-030 or 060) as a conductive substrate was cut into 50 × 200 mm and mounted on a rotating drum. The prepared slurry was applied to carbon paper mounted on a rotating drum by a spray method.

  The coating speed is 1 minute per 1 g of the solution, and 10 g per layer is applied, for a total of 3 layers. As shown in FIG. 2, the slurry is applied to one surface of the carbon paper and dried, and then the carbon paper is remounted on the rotating drum so that the other surface becomes the outer surface. Drying and remounting were performed, and the third coating and drying were performed on the surface where the first layer was already formed. Thereafter, firing was carried out at a firing temperature of 380 ° C. for 1 hour to obtain first and second water-repellent porous layers integrated with carbon paper.

  The side that was applied twice at this time was the first water-repellent porous layer, and the side that was applied only once was the second water-repellent porous layer.

<Production of third water-repellent porous layer>
As the third water-repellent porous layer, a commercially available carbon cloth with a water-repellent porous membrane (manufactured by BAFS: LT-2300W or LT-2500W) was used. The water repellent porous film contains a carbon material and polytetrafluoroethylene, and is formed on one side of a carbon cloth.

<Preparation of anode catalyst layer>
A carbon particle carrying platinum ruthenium alloy fine particles, a perfluorosulfonic acid polymer solution (Nafion solution DE2020 manufactured by DuPont) and a solvent are mixed with a homogenizer to prepare a slurry having a solid content of about 15%. The coating was applied to one surface using a die coater. And this was dried at normal temperature, it peeled from the base material, and the anode catalyst layer was formed.

<Preparation of cathode gas diffusion layer>
Carbon paper (TGP-090 manufactured by Toray Industries, Inc.) having a porosity of 75% was prepared as a cathode gas diffusion layer.

<Preparation of cathode catalyst layer>
Carbon particles carrying platinum fine particles, a perfluorosulfonic acid polymer solution (Nafion solution DE2020 manufactured by DuPont) and a solvent were mixed with a homogenizer to prepare a slurry having a solid content of about 15%. The obtained slurry was applied to one surface of the substrate using a die coater. And this was dried at normal temperature, it peeled from the base material, and the cathode catalyst layer was formed.

<Preparation of electrolyte membrane>
A solid electrolyte membrane Nafion 112 (manufactured by DuPont) containing a perfluorosulfonic acid polymer was prepared as an electrolyte membrane.

<Production of membrane electrode assembly (MEA)>
The electrolyte membrane and the cathode catalyst layer were overlaid, and the cathode gas diffusion layer was overlaid on the cathode catalyst layer, and pressed under conditions of a temperature of 135 ° C. and a pressure of 40 kgf / cm ² . Subsequently, an anode catalyst layer is stacked on the opposite side of the electrolyte membrane on which the cathode is stacked, and further, the first water-repellent porous layer, the carbon paper, the second water-repellent porous layer, A carbon cloth with a water-repellent porous film (third water-repellent porous layer) was superposed and pressed under conditions of a temperature of 135 ° C. and a pressure of 10 kgf / cm ² to prepare a membrane electrode assembly (MEA). The water repellent porous film of the third water repellent porous layer was brought into contact with the second water repellent porous layer. The electrode area was 12 cm ² for both the cathode and the anode.

<Assembly of fuel cell>
Subsequently, a fuel cell having the configuration shown in FIG. 3 was produced using this membrane electrode assembly. Specifically, this membrane electrode assembly was sandwiched between gold foils having a plurality of openings for taking in air and vaporized methanol, thereby forming an anode conductive layer and a cathode conductive layer.

  The laminate in which the membrane electrode assembly (MEA), the anode conductive layer, and the cathode conductive layer were laminated was sandwiched between two resin frames. A rubber O-ring was sandwiched between the cathode side of the membrane electrode assembly and one frame, and between the anode side of the membrane electrode assembly and the other frame, respectively.

  Moreover, the frame on the anode side was fixed to the fuel distribution mechanism by caulking and screwing through a gas-liquid separation membrane. A 0.2 mm thick silicone sheet was used for the gas-liquid separation membrane. On the other hand, a water vapor permeation suppression layer was formed on the cathode side frame. On this water vapor permeation suppression layer, a stainless steel plate (SUS304) with a thickness of 2 mm formed with air inlets (4 mm diameter, 64 holes) for air intake is arranged to form a cover plate, and screws Fixed with a stop.

(Example 2)
A fuel cell having the same configuration as that described in Example 1 was prepared except that carbon paper was used instead of carbon cloth as the conductive substrate of the third water-repellent porous layer.

(Comparative Example 1)
Explained in Example 1 described above, except that the air resistance of the third water repellent porous layer is larger than the total value of the air resistance of the first and second water repellent porous layers. A fuel cell having the same configuration as that described above was produced.

(Comparative Example 2)
The same configuration as that described in Example 1 except that the air resistance of the second water repellent porous layer is larger than the air resistance of the first water repellent porous layer. A fuel cell was prepared.

(Comparative Example 3)
The air resistance of the second water-repellent porous layer is made larger than the air resistance of the first water-repellent porous layer, and the air resistance of the third water-repellent porous layer is increased. A fuel cell having the same configuration as that described in Example 1 was prepared except that it was made larger than the total value of the air resistance of the first and second water repellent porous layers.

(Comparative Example 4)
As shown in FIG. 9, a fuel cell having the same configuration as that described in Example 1 was prepared except that carbon paper 32 was used as the anode diffusion layer.

Pure methanol is injected into the liquid fuel storage chamber of the fuel cell formed as described above, and the initial output value (mW / cm ² ), the output value after continuous operation (mW / cm ² ) and the output are maintained under the following conditions. The rate (%) was measured, and the results are shown in Table 1 and FIG.

A method for measuring the initial output value (mW / cm ² ) will be described below.

  The fuel was fed to the fuel distribution mechanism in a configuration using a pump from the fuel storage chamber. This fuel cell was measured at a constant voltage of 0.35 V at a control temperature of 45 ° C., and the output value 10 hours after the start of measurement was used as the initial output.

A method for measuring the output value (mW / cm ² ) after continuous operation will be described below.

  The same constant voltage measurement as described above was performed, and the output value when continuous measurement was performed for 1000 hours from the start of measurement was defined as the output value after continuous operation.

  A method for measuring the output retention rate (%) will be described below.

  From each value obtained by the above measurement, an output maintenance rate is obtained by calculation according to the following formula.

Output maintenance ratio (%) = (Output value after continuous operation / Initial output value) × 100

  As is clear from Table 1 and FIG. 13, it can be seen that the fuel cells of Examples 1 and 2 have higher initial outputs, output retention ratios, and output values after continuous operation than those of Comparative Examples 1 to 4.

  10 to 12 schematically show the fuel and water distribution of the first to third water-repellent porous layers in Examples 1 and 2 and Comparative Example 2. FIG. As shown in FIGS. 10 and 11, according to Examples 1 and 2, more water can be retained in the first water-repellent porous layer. In particular, as shown in FIG. 10, in Example 1, the amount of fuel retained in the first water-repellent porous layer 9 is sufficiently narrowed, and the water retaining property of the first water-repellent porous layer 9 is excellent. Therefore, crossover can be suppressed and output performance is improved.

  On the other hand, in Comparative Example 2 shown in FIG. 12, the amount of water retained in the vicinity of the anode catalyst layer 7 was smaller than that in Examples 1 and 2, and the output performance deteriorated.

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly (MEA), 2 ... Electrolyte membrane, 3 ... Cathode (air electrode), 4 ... Anode (fuel electrode), 5 ... Air electrode catalyst layer, 6 ... Air electrode gas diffusion layer, 7 ... Fuel electrode Catalyst layer, 8 ... Fuel electrode gas diffusion layer, 9 ... First water-repellent porous layer, 10 ... Conductive substrate, 11 ... Second water-repellent porous layer, 12 ... Third water-repellent porous layer , 20 ... Fuel distribution mechanism, 21 ... Fuel container, 22 ... Flow path, 23 ... Cover plate, 24 ... O-ring, 25 ... Fuel discharge port, 26 ... Pump, 27 ... Fuel injection port, 28 ... Fuel distribution plate, DESCRIPTION OF SYMBOLS 29 ... Gap part, 31 ... O-ring, 32 ... Fuel electrode gas diffusion layer, 101 ... Measurement end, 102 ... Measurement sample, 103, 108, 111, 113 ... Narrow tube, 104 ... Water column pressure gauge, 105 ... Side pressure chamber (B Chamber), 106 ... nozzle, 107 ... constant pressure chamber (A chamber), 109 ... external compression source, 110 Pressure gauge, 112 ... room G.

Claims (4)

A cathode catalyst layer;
An anode catalyst layer;
An electrolyte membrane disposed between the cathode catalyst layer and the anode catalyst layer;
An anode gas diffusion layer including first to third water-repellent porous layers laminated on the anode catalyst layer,
The air permeability resistance of the first water repellent porous layer is larger than the air resistance resistance of the second water repellent porous layer, and the first water repellent porous layer and the second water repellent porous layer. A fuel cell characterized in that the total air resistance of the aqueous porous layer is larger than that of the third water-repellent porous layer.   The first water-repellent porous layer is integrated on one surface, and a conductive base material on which the second water-repellent porous layer is integrated on the other surface is further provided. The fuel cell according to claim 1.   The fuel cell according to claim 1, further comprising a conductive base material on which the third water-repellent porous layer is integrated.   The fuel cell according to any one of claims 1 to 3, wherein the conductive substrate on which the third water-repellent porous layer is integrated is a carbon cloth film.

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